In recent years, problems relating to water damage to asphalt pavement have caused researchers to direct their attention toward a phenomena referred to as "stripping". This term is applied to asphalt pavement mixtures that exhibit separation of the asphalt concrete from the aggregate surfaces due primarily to the action of water on the asphalt over time under various environmental conditions. It should be noted that asphalt concrete generally consists of about 95% stone and about 5% asphalt cement.
Asphalt may be generally described as a dark-brown to black cementitious material, solid or semi-solid in consistency, in which the primary constituents are a mixture of paraffinic and aromatic hydrocarbons and heterocyclic compounds containing sulfur, nitrogen and oxygen. As discussed in The Asphalt Handbook (The Asphalt Institute, Manual Series No. 4, 1965 ed.), incorporated herein by reference, various grades of asphalt may be produced by selecting different processing conditions. In this regard, two basic types of solid asphalt, asphalt cement and air-blown asphalt, and two basic types of liquid asphalt, cutback asphalt and emulsified asphalt, are utilized commercially. Asphalt cement is defined as asphalt which has been refined to meet paving or industrial specifications, cutback asphalt is asphalt cement which has been liquified by blending with petroleum solvents; and asphalt emulsions are prepared such that the asphalt or flux in the emulsion base is emulsified in the inner phase (an oil-in-water type emulsion). The emulsion can also be of the water-in oil type in which water constitutes the inner phase (see Jellsten et al, "Asphalt Compositions Having Improved Adhesion To Aggregate", U.S. Pat. No. 3,928,061). The present invention is believed to be useful in connection with all such asphalts.
The particle size of mineral aggregate used in an asphalt composition may vary over a wide range, such as from 2.times.10.sup.-5 to 6.times.10.sup.-2 meters in diameter, or the aggregate may be of a fairly uniform size. Mineral aggregates employed in asphalt compositions also range in character from hydrophilic to hydrophobic. It has long been known that mineral aggregates have a greater attraction for water than for oil or asphalt. In general it can be said that siliceous and acidic minerals such as sands and gravels tend to be very hydrophilic whereas calcareous and alkaline materials such as limestone tend to be slightly hydrophilic. It is difficult, therefore to obtain and maintain a satisfactory asphalt coating on the mineral aggregate particles when water is present. One example of an asphalt composition is the combination of asphalt cement with a size-graded mineral aggregate. This combination is referred to as asphalt concrete and is used in road paving applications. A poor asphalt coating on the mineral aggregate leads to break up of the asphalt concrete and commonly results in potholes and pavements which are unserviceable.
One common method of pavement construction is to remove water from the aggregate by forced evaporation prior to coating with asphalt cement. In practice, this requires a certain amount of aggregate drying time which consumes energy and may result in a lengthened construction period. If weather conditions are unfavorable, such as during periods of rainfall or high humidity, road construction may be severely hindered if not halted. Even if the water is removed and the asphalt successfully deposited onto the aggregate, the asphalt coating may ultimately be degraded by the action of groundwater or rainfall.
A successful method of increasing pavement life has been to add one or more antistripping additives to the asphalt compositions. Such additives increase the hydrophobicity of the aggregate, thereby strengthening and preserving the asphalt-aggregate bond. While antistripping additives have been found to be successful in certain paving and roofing applications, conventional asphalt compositions employing such additives are still limited in that the strength of the asphalt-aggregate bond is often not sufficient to resist damage from prolonged conditions of stress and wear.
U.S. Pat. No. 4,639,273 discloses formaldehyde adducts of amines, polyamines and amides which are employed in asphalt compositions in order to improve the overall adhesion between the asphalt and aggregate.
U.S. Pat. No. 4,430,172 discloses an ethoxylated amine asphalt antistripping agent. The antistripping agent is disclosed as providing adhesion between aggregate materials and the bitumen containing material.
U.S. Pat. No. 3,963,509 discloses asphalt which is indicated as having high adhesion strength. The asphalt is prepared by incorporating into the asphalt a small amount of a monocarboxylic chromic chloride.
U.S. Pat. No. 3,933,710 discloses a latex-asphalt emulsion composition. The composition is comprised of a cationic latex prepared by the emulsion-polymerization of a diene in the presence of an emulsifier of an inorganic or organic acid salt of an N-alkylpropylene diaminepolyglycol ether.
U.S. Pat. No. 3,928,061 discloses asphalt compositions which are provided with improved adhesion to the aggregate. The compositions being comprised of an alkyl oxyalkylene amine and, optionally, an alkanolamine.
U.S. Pat. No. 3,861,933 discloses an asphalt which is indicated as having high adhesion strength. The asphalt is prepared by incorporating therein a small amount of an aminoalkyl polyalkoxysilane.
U.S. Pat. No. 4,430,465 discloses an asphalt composition which is made by mixing together asphalt and an alkadiene-vinylarene copolymer and a petroleum hydrocarbon resin and an amine-based antistripping agent.
U.S. Pat. No. 3,615,797 discloses a method of making an asphalt composition having high adhesion properties. The adhesion properties are apparently improved by the incorporation of small amounts of an ethylene oxide condensate of a long chain alkyl triamine compound.
U.S. Pat. No. 2,759,839 discloses asphalt compositions which include small amounts of an oil-soluble tertiary amine compound.
Long chain polyamine compounds per se are disclosed within numerous publications such as U.S. Pat. No. 4,218,307 and U.S. Pat. No. 3,200,155. In addition, amine compounds obtained as a result of a MANNICH type reaction are known to be disclosed within the prior art.